1. Field of the Invention
The present invention relates to an AMTEC (alkali metal thermal-electric converter) with a heat pipe and more particularly, to an AMTEC with a heat pipe minimized a heating part and a condensation part of the AMTEC, and improved in efficiency of thermal to electric conversion through installing the heating and cooling heat pipes as a heating device and a condensing device in the AMTEC, in which a metal fluid is heated by a latent heat of an operating fluid of the heat pipe, instead of heat conduction from a heat source, thereby reducing a temperature difference needed for heat transfer to increase a vapor generation of the metal fluid by the heat source of a lower temperature than a conventional heat source; improving a cooling performance in a condensation part to result in a high efficiency of thermal to electric conversion; and using no additional driving components for driving the heat pipe.
2. Description of the Related Art
An AMTEC (alkali metal thermal-electric converter) is a device having a characteristic of directly converting thermal energy to electrical energy. In the AMTEC, when a temperature difference ΔT is applied to both ends of a BASE (beta-alumina solid electrolyte) having ion conductivity, a difference in vapor pressure of liquid Na filling the inside of a cell acts as a driving force to move Na+ ions through a space among loosely bonded lattice oxygen. The Na+ ions passing through the electrolyte are neutralized on the surface of an electrode during a condensing process, to generate electricity. Then, the electricity of a low voltage and a high current is output. High capacity generation is enabled by modulating and collecting the low voltage and high current electricity.
The principle of the AMTEC technology is that, when alkali metal sodium is vaporized in a vaporizer of a high pressure region by a heat source, sodium ions pass through the BASE and free electrons pass through electrical load from positive pole and return to negative pole to re-combine with the ions coming from the surface of the BASE of a low pressure region, thereby generating electricity. The neutral sodium vapor is condensed by cooling of a low temperature fluid in inner surface of a condenser of a low pressure region, and the condensed liquid returns to the vaporizer by a condenser wick to complete a cycle. The typical temperatures of the vaporizer and condenser of the metal fluid are respectively 900˜1100K and 500˜650K. The vaporization and condensation of sodium in these temperature conditions enables the efficiency of generating electricity by the thermal to electric conversion up to 40%.
A semiconductor thermoelectric generation system has been used as a power source for space application but there are drawbacks of low efficiency and heavy weight in such a generation system. The AMTEC technology is developed to substitute the thermoelectric generation system using a thermoelectric module. The characteristics of the AMTEC technology are to have high power density, high efficiency and low cost per unit area and to maintain stability during use. The AMTEC technology has the high a higher conversion efficiency compared to any other direct thermo-electric converters and directly converts heat energy to electric energy using various heat sources, such as fossil fuel, solar energy, radioactive isotopes, nuclear reactors or the like, as its fuel.
Unlike the conventional electricity generation technology, the AMTEC technology is the high efficiency technology relating to the thermal to electric converter, using the heat sources, such as not only the heat of combustion of gas but also waste heat, solar heat, heat of the earth, radioactive isotopes or the like, without a driving part, such as a turbine or boiler. Therefore, the AMTEC technology is considered as the new future-oriented technology of electricity generation, which is capable of producing high capacity electricity of several hundred MWs. Specifically, since the power density per mass is about 2˜3 times that of a solar power generator or Stirling engine, the AMTEC technology can be widely used for space application, military application, and power technology using high temperature waste heat. Further, since the AMTEC technology uses the condenser wick for circulation of a liquid metal, mechanical elements are not needed, to increase a stability of the converter.
Since the AMTEC technology has the high capacity of MWs in high efficiency, it may be used for the thermo-electric converter. Further, when the AMTEC technology is used for the cogeneration (combined heat and power), it is capable of improving the utilization of energy by 70% or more. Therefore, the research and development of the AMTEC technology are needed to generate power with no noise, to increase the effective utilization of energy, and to reduce the peak load.
The aforementioned AMTEC comprises: sodium as a metal fluid, a BASE (beta alumina solid electrolyte) for separating a system into a high pressure region and a low pressure region and allowing only sodium ions to pass to generate electricity, a condenser for condensing and absorbing sodium vapor, a condenser circulation wick for circulating liquid sodium, a vaporizer for converting sodium transferred from the condenser circulation wick in the liquid state into the vapor state, and a heater for heating sodium as a heat source.
The AMTEC receives heat from the heat source outside and transfers the heat to the vaporizer inside. In the conventional AMTEC, since heat is supplied to the inside of the vaporizer by conduction, a temperature difference needs to be high and thus, the temperature of the heat source needs to be high. Further, since the conventional condenser releases heat by conduction, there is a problem in that the AMTEC is large in size. Consequently, the efficiency of generating electricity by the thermal to electric conversion decreases.
Moreover, in the AMTEC, since heat supply to vaporize the metal fluid is performed by conduction, a temperature difference needs to be high and thus the temperature of the heat source needs to be high. Further, since the condenser for condensing the metal fluid vapor operates by conduction, there is a problem in that the heat conduction area increases.